I've been dating my girlfriend for just a few months now and I recently took her to a local car show. It was a nice July evening and then sun was setting as we quickly walked among some classic cars. At one point she turned to me and said something along the lines of "because of you I pick out all of the swirl marks in cars now." This made me think of two things immediately, I have an awesome girlfriend and even car enthusiasts might not fully understand swirl marks.
Most modern cars have multiple layer paint systems. Let's take your cars hood for instance. That hood starts out as a piece of metal or fiberglass which a primer is sprayed onto. Following the primer is your paint, the actual color of your car. On top of these layers is the clear coat which does two things, protects the color of the car and adds the gloss to the paint.
So what are swirl marks? Swirl marks are circular scratches in the clear coat of your vehicle. These marks are caused by various elements from abrasive towels to the self wash down the street. Over time your car accumulates these marks and it dulls the paint and takes away from the shine. You might be asking yourself "but my cars surface is hard how does it get scratched by something like a cotton cloth?"
Every car manufacturer uses different types of paint or clear coats and all of these coats come in varying hardness. With that being said they all have the ability to be scratched...we aren't talking about diamonds here, these coats are still soft enough to be damaged. These scratches aren't generally deep which is good news because that means we can fix them.
I like to use this picture as an example because there is such a nice contrast. This was an STI I did a full paint correction on (trying to remove as many swirl marks and other marks as possible). Look at the gorgeous blue Subaru paint, it really pops when the swirl marks are removed. If you take notice especially around the reflections of the work lights the paint is very dull and has a white hue to it. This is caused by all of those nasty swirls!